First Detection of Molecular Gas in the Shells of CenA

TL;DR

This study reports the first detection of molecular gas in the shells of the galaxy CenA, challenging existing theories and suggesting that gas dynamics and star formation can occur far from galactic centers.

Contribution

It provides the first observational evidence of molecular gas in galaxy shells, indicating complex gas dynamics and star formation far from the nucleus.

Findings

Molecular gas (CO) detected 15 kpc from galaxy center

CO to HI emission ratio similar in shells and core

Gas dynamics consistent with clumpy interstellar medium

Abstract

Shells are faint arc-like stellar structures, which have been observed around early type galaxies and are thought to be the result of an interaction. HI gas has recently been detected in shells, a surprising result in view of the theoretical predictions that most of the gas should decouple from stars and fall into the nucleus in such interactions. Here we report the first detection of molecular gas (CO) in shells, found 15kpc away from the center of NGC5128 (CenA), a giant elliptical galaxy that harbors an active nucleus (AGN). The ratio between CO and HI emission in the shells is the same as that found in the central regions, which is unexpected given the metallicity gradient usually observed in galaxies. We propose that the dynamics of the gas can be understood within the standard picture of shell formation if one takes into account that the interstellar medium is clumpy and hence not highly dissipative. The observed metal enrichment could be due to star formation induced by the AGN jet in the shells. Furthermore our observations provide evidence that molecular gas in mergers may be spread out far from the nuclear regions.